Generally, a flow path control valve for controlling a flow path for a circulating fluid is used in hydraulic pressure generating apparatuses including hydraulic pumps, hydraulic actuators, and pumps. Such a flow path control valve is used in air conditioning facilities, automation facilities or the like so that it can control a flow path through automatic operation thereof or depending on operation conditions in accordance with hydraulic pressure generating apparatuses.
FIGS. 1 and 2 are views showing heating and cooling systems established by a heat pump type air conditioner employing a conventional flow path control valve. As shown in FIG. 1, when the heat pump type air conditioner is used as a cooling system, the heat pump type air conditioner comprises a compressor 10 for compressing a working fluid at medium temperature and low pressure to be the working fluid at high temperature and pressure; an outdoor heat exchanger 20 for heat-exchanging the working fluid at high temperature and pressure, which has been compressed by the compressor 10, with external air so as to be condensed into the working fluid at low temperature and high pressure; a first expansion valve 30 for decompressing the working fluid at low temperature and high pressure, which has been discharged from the outdoor heat exchanger 20, to be the working fluid at low temperature and pressure; and an indoor heat exchanger 40 for heat-exchanging the working fluid at low temperature and pressure, which has been expanded in the first expansion valve, with room air so as to be the working fluid at medium temperature and low pressure through phase change. Further, a first check valve 32 for preventing a back flow of the working fluid is installed between the first expansion valve 30 and the outdoor heat exchanger 20.
The heat pump type air conditioner can also heat a room by controlling a flow path for the working fluid, as shown in FIG. 2. To this end, a 4-way valve 50 for changing the flow path for the working fluid is installed on a discharge side of the compressor 10. Meanwhile, the working fluid at high temperature and pressure, which has been compressed by the compressor 10, is reverse circulated through a flow path changed by the 4-way valve 50. The working fluid at high temperature and pressure, which is reverse circulated in such a manner, is heat-exchanged with the indoor heat exchanger 40 to be the working fluid at low temperature and high pressure. Meanwhile, in the heating operation of the air conditioner, the first expansion valve 30 is closed, and the working fluid at low temperature and high pressure passes through a second check valve 37 parallel connected to the first expansion valve 30. The working fluid, which has passed through the second check valve 37, then passes through a second expansion valve 35 to be the working fluid at low temperature and pressure. The working fluid, which has passed through the second expansion valve 35, is heat-exchanged with the outdoor heat exchanger 20 to be the working fluid at medium temperature and low pressure, and then returned to the compressor 10 via the 4-way valve 50. Further, an auxiliary condenser 25 for lowering the temperature of the working fluid is installed between the first expansion valve 30 and the first check valve 32. To this end, the flow path is formed with a branch line to supply the working fluid to the auxiliary condenser 25, and a first solenoid valve 26 for controlling the circulation of the working fluid is installed at a trailing end of the branch line. Further, a second solenoid valve 27 for controlling the inflow of the working fluid upon forward circulation of the working fluid is installed between the second check valve 37 and the auxiliary condenser 25, and a third check valve 28 for preventing a back flow of the working fluid is installed at the rear of the second solenoid valve 27.
Next, FIG. 3 that is a view showing a variation in a part of such a conventional heat pump type air conditioner will be described below. In the conventional air conditioner, as shown in FIG. 3, refrigerant vapor compressed by the compressor 10 is discharged to a single conditioner 31a to which parallel conduits 41 and 42 are connected, and an air-cooling type heat exchanger 45 or water-cooling type heat exchanger 46 is separately installed at one of the parallel conduits 41 and 42 according to the type of condensing the working fluid. At this time, in case of the air-cooling type heat exchanger 45, heat of condensation produced when the working fluid such as a refrigerant is condensed with ambient air heats the air that in turn will be used for convection heating or the like. In case of the water-cooling type heat exchanger 46, heat of condensation produced when the working fluid is condensed with water generates hot water that in turn will be used for condensing heating, hot water supply or the like. Then, the working fluid that has been selectively branched is supplied to a single conduit 31b to establish a circulation cycle.
Meanwhile, upon selective operation of the air-cooling type heat exchanger 45 or the water-cooling type heat exchanger 46, respective solenoid valves 43 installed at inlets d the air-cooling type heat exchanger 45 and the water-cooling type heat exchanger 46 are controlled to be selectively opened or closed, so that the working fluid can be selectively supplied to one of the parallel conduits 41 and 42. Here, since the solenoid valve 43 is constructed to be opened or closed under control according to a detection value from a sensor installed at the air-cooling type heat exchanger 45 or the water-cooling type heat exchanger 46, the sensor malfunctions upon occurrence of a back flow of the working fluid, resulting in incomplete selective opening or closing d the flow path and lowered reliability of the operation d the solenoid valve 43.
FIG. 4 is a sectional view of the solenoid valve used for the conventional heat pump type air conditioner. The solenoid valve 26, 27 or 43 comprises a housing 51 formed with a valve chamber 52 that can be in fluid communication with an inlet 52 and an outlet 56, an opening/closing member 58 installed movably within the valve chamber 52 for moving between an opening position and a closing position to open or close a passage between the inlet 54 and the outlet 56, an elastic member 59 installed within the valve chamber 52 to bias the opening/closing member 58 toward the closing position, and a solenoid 60 installed at a side of the housing 51 to electromagnetically moving the opening/closing valve 58. When the solenoid valve is supplied with electric power, the opening/closing member 58 is moved to the opening position by means of excitation force from the solenoid 60. When the excitation force from the solenoid 60 is removed, the opening/closing member 58 is moved to the closing position by means of restoring force from the elastic member 59.
However, if pressure of the working fluid acting in a reverse direction when the conventional solenoid valve 26, 27 or 43 is closed increases, there may be a case where the opening/closing member 58 of the solenoid valve is opened. To prevent this in the prior art, the check valves 28 and 44 are installed at the rears of the solenoid valves 26, 27 and 43 to prevent a back flow of the working fluid. Therefore, since the check valve should be additionally installed at the rear of the solenoid valve to prevent the back flow of the working fluid in the prior art, it results in a complicated structure. Particularly, an air conditioning system employing a large number of solenoid valves and check valves has problems in that its structure is complicated and the number of parts increases, resulting in increased costs.